Production of sulphuric acid by the contact process



C. B, CLARK Jan. 21, i936.

PRODUCTION OF SULPHURIC ACID BY THE CONTACT PROCESS FiledJune 6, 1953 2 Sheets-Sheet l ATTORNEY.

c. B. CLARK 2,028,733

THE CONTACT PROCESS Filed June e, 195s Jan. 2l, 1936.

PRODUCTION OF SULPHURIC ACID BY 2 Sheets-Sheet 2 lNvENToR. CWP/.4 C24/PA,

ATTORNEY.

(Hmm) Patented Jan. 21., 1.936

PATENT OFFICE PRODUCTION OF SULPHURIC ACID BY THE CONTACT PROCESS Cyril B. Clark, Scarsdale, N. Y., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine Application June (i,v 1933, Serial No. 674,489

10 Claims.

This invention relates to the production of sulphuric acid by the contact process using SO2 gases containing hydrocarbons or other hydrogen containing substances, and more particularly to 5 the production of sulphuric acid by a contact process using SO2 gases obtained by the thermal decomposition of sulphuric acid sludges from the sulphuric acid purification of carbonaceous material such as, for example, petroleum products. Petroleum refineries using strong sulphuric acid as a solvent and reagent in the purification of the various petroleum fractions produce large quantities of so-called acid sludge, which is a mixture of sulphuric acid and various partly or Wholly sulphonated organic compounds together with a considerable amount of hydrocarbons which are present in solution. This sludge in most communities cannot be used as a fuel because of the sulphur dioxide given off in burning which constitutes a serious nuisance and even in isolated communities presents a serious corrosion problem in the burner equipment. For this reason the sludge has proved to be a waste product, the disposal of which has created a considerable problem. Moreover, it contains large amounts of sulphur in combined form which, of course, is normally wasted. Various attempts have been made to produce SO2 from this acid sludge by different methods using distillation. Up to the present time the only commercially successful method is that described in the application of I. Hechenbleikner, Serial No. 568,050, led October l0, 1931 now Patent No. 1,953,225 dated April 3, 1934. In this process the acid sludge is thermally decomposed by means of combustion gases which contact directly with the sludge inside a rotary kiln. Other processes include the use 'of an externally fired rotary kiln with a fluid sludge which is maintained con- 40 tinuously in a fluid state.

All of the processes produce SO2 from acid sludge by thermal decomposition and result in a gas which contains not only SO2, but considerable amounts of water and various hydrocarbons together with a considerable portion of carbon dioxide and sometimes nitrogen particularly in the Hechenbleikner process when combustion gases are employed. Normally this SO2 gas is subjected to cooling or refrigeration in water cooled condensers followed by drying in drying towers usually by means of sulphuric acid which results in the condensation and removal of water and of the heavier condensable hydrocarbons.Y

After leaving the drying tower, the amount of free water vapor is normally of the order of 2 milligrams per cubic foot of gas, but there is a very considerable quantity of uncondensable or difficulty condensable hydrocarbons and other hydrogen containing gases. W'hen these gases pass through a sulphuric acid converter they are, 5 of course, oxidized producing water as one of the products.

The presence oi water in the gases in amounts greater than 25 to 30 milligrams per cubic foot, which means the presence of from 21/2 to 3 milli- 10 grams of hydrogen per cubic foot, causesa serious problem because when the water content of the converted gases leaving the sulphuric acid converter exceeds 25 to 30 milligrams per cubic foot, on cooling it unites with some of the sulphur 15 trioxide to Iormsulphuric acid mist. This acid mist is strongly corrosive if it is permitted to further condense out on the walls of the equipment, and it cannot be completely absorbed by the sulphuric acid in the normal absorbing tower. 20 This gives rise tofumes which are highly corrosive to exhaust stacks and constitute quite a serious nuisance.

In order to avoid the diilculty encountered by the presence of hydrocarbon gases in the SO2 25 coming from an acid sludge still and similar gases containing hydrogen or hydrocarbons various methods can be employed, thus, for example, the Hechenbleikner application, above referred to, suggests the complete removal of hydrocarbon 30 gases. In my co-pending application Serial No. 670,123, led May 9, 1933, I have described a process in which the removal of the hydrocarbon gases is only partial, keeping the hydrogen content below 21/2 to 3 milligrams per cubic foot. 35 Other methods of overcoming this serious diiculty include the combination of an acid sludge still with another source of sulphur dioxide, such as a sulphur or ore burner. This combined process which dilutes the hydrocarbons in the SO2 40 gases from the acid sludge still is described and claimed in my co-pending application Serial No. 671,647, iiled May 18, 1933.

Methods which involve partial or total removal of the hydrocarbon gases or dilution by admixture 45 with SO2 gases from other sources, while effective, either require additional equipment, which in some cases may be quite expensive, or require a market for acid of such character that a large portion of the SO2 may be obtained from sulphur 50 or ore burners( For these reasons the various processes of acid sludge decomposition have lacked exibility and in some cases have been unnecessarily costly.

SO2 gases from distillation of acid sludge con- 55 Ytain hydrocarbons of necessity, but it is desirable in'lsomecases' to deliberately add hydrocarbons certain SO2 gases, namely gases that are very weak in SO2. In order that aconvertermay operate, satisfactorily, the concentration SO2 must be suiiiciently high to generate enough heat tonkeep the reaction going., vNormally 31/2% SO2 is about the lower limit which can `beused with- 'ut external heat, vand evenrwith a'gas of this of the hydrocarbons Vwill rcompensate for gases decient in SO2. even a fraction of a percent of hydrocarbons will add suicie'ntly tcthejheat'evolution of a weak SO2 gas so that satisfactory converter operation may be obtained. In the past, however, this sim-V ple method of dealing with dilute SOngases *hasYY not been used to any considerable extentbecause the burning of hydrocarbons generates suflicient waterto; raise difficulties due to the formation oi acid mist. YIt isvan advantageof the present invention that it may beappliedto weak SOzgases which have been fortified by the addition of sutilcie'nt hydrogen or hydrocarbon containing gasesV to provide adequate Vheat in the converter.

According to the presentinvention theY disad-V vantages involved inthe vpresence of Yhydrogen Y ebntaininggases in .SOz are overcome without requiring elaborate equipment or very Ycareiul operating conditions, the latter being an importantVA Y factor as the gas from an acid sludge still is rarely l uniform particularly in `batch processes vand shows Yconsiderable variationY because Vof fluctuating sludge'composition, even in the rnost highly ein- .cientcontinuous processes such asA that described in the Hechenbleikner application, above referred nato,` This requirescontinualadjustment and very Y 'ycarefulsupervisionV ifV the hydrocarbon gas con tent is to be kept continually below 2 1/gto 3 milli-VV grams perscubic foot. Y According tothe present invention no attempt is made to reduce the content-of Vhydrogen containing gases below any particular limits and an SOrgaswhich hasmerely Ybeen dried,r is` sent directly through the converter.

Acid mist is kept from'corroding'the equipment byrnaintaining the gas stream between converter and abserber at a temperature above that of theY Y dew point for the Yacidmist,` that is to say above about l55) to 600 At thistempel'ture no'acid f mistseparates out and Ymost of the S03 can be absorbed. -The vacid mist formed inthe absorber is, of course, incompletely absorbed and passes out of the absorber in considerable quantities. I l

' have found, however, that even the large amounts of; acid mist 'which is formed when an SO2 gas from the distillation of acid sludge isusedgcanv heprecipitated electrically or mechanically by Cottrell; precipitatorsyor coke ltersV and no difficulty is `encountered due to corrosion of they er;`-

fhausyt stack and no fume nuisance is created.

The present invention which acts directly con-V trary to the procedure hitherto adopted in the utilization of SO2 gases from the distillation of.

Y Aacid sludge and similar sources/avoids allfth'e tion with a minimum or". skilled supervisionfand f at the same tirnejd'oesnot present any nuisance or corrosion problems. Since nol attempt is made 1 w. to4 maintain any particularconcentration of hy 'drogenv containing eases in; the YSO2 stream, the

adsense v Y' n:

Thus (for example a percentor 'd' d 1 while the present invention will handle .the gases from anytypeof sludge'it shouldbe noted thatY s Vsince there isno removal of hydrogen containing materials substantially all of thehydrogen which.` Y

is transformed into water is absorbedV in the acid 20 operation of the process is unaffected by fluctuav f tions in sludge composition or other operating conditions of the sull; The mist precipitator .is

automatic'in its operation and is of suiicient ca- Y pacity so that iiuctuations in the amount ofinist produced do not haverany deleterious effect and vCR require no'adjustment orV other careful operatingV control.

The invention is particularly applicable to theYY Y.

l() Y Y* l use of SO2 gases Vfrom petroleum acid sludge, but,

ofcourse, may be us'edwith SO2 from sludgesVKV from thefpurification of other carbonaceous ma-Vvr Yteria'l'.v The aniountof `hydrecarbon will, of

course, vary withthe character fof the sludge and systenr and, therefore, enters as a'factork in the V,Waterbalance of the system. Where'tlie amount of Yhydrocarbon'gases.is very high, the `amount of water' produced may in certain caseseX-ceed that requiredrrfor reaction with the SrOafrorn'the converter, particularly when it is borne in mind that normally the acid from thefdryingtower forms part ofthe vsystem. In cases whereV thewater ls greater thanmthat suicient to produce the desired Y strength of acid, it maybe neeesslary to remove .s A'

:3Q Yor all'oikthe drying tower acid from the circuit.

a part of the hydrocarbon gasesorto take out part This latterv procedure, whichfthe excess diluted drying'tower acidis recirculated through the acid .sludge still, is'described'in an application of I.

Hechenbleikner/Se'rial No. 574,244, filed Novem-Y ber 11,` 1931, now Patent Y2,001,359, issued May 14j,

what lowered in a modification .of the present invention', the hydro'carleon removing equipment isY not entirely dispensed vwith as in the preferred Ymodification where allrof the hydrocarbon gases remainin the stream. Despite the fact that the 1935.1 yWhen vthe hydrocarbon content is somehydrocarbon removing equipment is not entirely eliminated jin such a modification, it neverthe-Y less representsa distinctY operating improvement over the systems in Ywhich'the hydrocarbon gasesk i are entirely removed or are brought down below an extremelyvlow maximum. Since' it is oniy necessary to assure ra rough removal of excess`Y V.lflydrocarbon gases so that the amount present will l not overload the entire acid circulating system, it

iis, of course, unnecessary to control'theremoval The presentfinvention may,` of course, be Vln- Ycluded in a combined process using SO2 from acid Y s' sludge and from the burning ofA sulphurcont'ain- Y ing materialin a'single plant. `I-Iowevenrsuch speciiicmodification is not claimed in the present 'application'and thisY r'orms Ya specific portion of they subject matterof my'co-pending application Serial No.A 671,647, abc-ve referredto. Y

When YSO2 froman acid sludge deci)mpositionTV system operating *onV the Hechenbleikner process is Yused in the present invention` it is necessary*V Vto usera -heat exchanger in order to preheat the Ycold 'S02 gases before the latter enter theV converter. `Where dilute SO2 gases arefortified with" hydrocarbons they mayv beeitherV ccldrorhot,

depending upon the system employedfinobtainfing them. Alsofitis possible to obtain"hotga'sesl from an acid sludge decomposition Y process byA usingtheV method describedin .the co-'pending 75 l Y application of Rumple, Serial No. 701,137, led December 6, 1933, in which a stream of SO2 is built up by gases from an acid sludge kiln and recirculating them through a water cooled con-f denser and then through a heat exchanger or stove, finally passing them again through the kiln. This cyclic process builds up the SO2 over 80% and a small amount of the gases are bled continuously either before or after passing through the heat exchanger or stove and the kiln. They are, of course, at high temperature and a heat exchanger is unnecessary and the gases can be passed directly into the converter without further treatment except an addition of sucient air for the reaction. Wherever hot gases containing hydrocarbons or hydrogen can be employed, the heat exchanger is eliminated and no danger of corrosion arises. Where cold gases are employed necessitating the heat exchanger care should be taken that the gases from the converter passing through the heat exchanger are kept at a temperature above the dew point of the acid mist in order to obviate any danger of corrosion.

In the drawings Fig. 1 is an elevation of a sys tem taking SO2 gases from a sludge distillation kiln operating under the Hechenbleikner process; and

Fig. 2 is an elevation of a system taking weak SO2 gases from a smelter and enriching them by the addition of hydrocarbon or hydrogen containing gases.

Airis blown by the blower I into a combustion furnace 2 in which carbonaceous or sulphur containing material may be burned. The combustion gases pass into the rotary kiln or retort 3 through which a stream of acid sludge passes from the sludge inlet 4 to the outlet for distilled carbonaceous residue 5. It will be apparent that as the sludge flows slowly in countercurrent to the hot combustion gases it passes successively through zones of increasing temperature, the rst zone being at temperatures sufcient to distill olf water and lighter hydrocarbons and ,further zones being at temperatures high enough to cause rapid reduction of S04 containing compounds to SO2 while the last zone is at a temperature at which a readily granulatable fuel can be obtained. Discharge from 5 may be either continuous or intermittent. The gases from the still leave at the sludge inlet end through the pipe 6 passing into a water cooled condenser 7 where heavy hydrocarbons and water are condensed out in different layers. The heavy hydrocarbons being discharged through an oil boot 8 while the water flows out through a water boot 9. Cooling water is introduced through the pipe l0 and leaves through the pipe II.

The gases from the condenser pass through a relief valve I2 and after admixture with air through the v alved pipe I3 enter the drying tower I4 where they are subjected to scrubbing with sulphuric acid which is recirculated by means of the acid pump I5. The dehydrated gases pass out of the top of the tower through the meter IS into the suction of the blower II whence they are discharged through a heat exchanger I8 into the converter I9. The heat exchanger is heated in normal operation by a portion of the gases from the converter flowing through the pipe and out through the pipe V2l. Care is taken to prevent the temperature of the gases in the heat exchanger from dropping below the dew point for acid mist. The gas from the heat exchanger and directly from the converter then passes into absorber 22 where most of the S03 is absorbed by scrubbing with sulphuric acid which is circulated by means of the acid pump 23 through a cooler 24. The exhaust gases containing some acid mist pass out through pipe 25 into a Cottrell precipitator 26. If desired, the precipitator may be replaced by a coke filter. In order to start up the system it is necessary to supply heat to the heat exchanger I8 until a temperature is reached which will permit the ignition of the gas in the converter. This is eected by using a starting furnace 27 which connects into the pipe 20; This pipe is provided with a valve 30 and the pipe leading from the starting furnace is provided with a valve 3l. Exhaust heating gases leave the heat exchanger through the pipe 28 controlled by the valve 29. Of course, in starting up, valves 29 and 3I are opened and valve 3U is closed. As soon as normal operation is attained valve 39 is opened and valves 29 and 3l are closed. The acid mist condensed in the precipitator or coke lter is, of course, returned to the acid circulation system.

In the drawings in Fig. 2 the drying tower and converter system is exactly the same as in Fig. =1

1, and the same parts bear the same reference characters. Instead of taking gases from an acid sludge still, they are taken from a smelter or similar source cf weak SO2 gases (not shown) and enter through a pipe 34, passing through dust filter and scrubbing tower 36 where dilute sulphuric acid is circulated by means of the acid pump 37. From the scrubber the gases pass through pipe 38 into the drying tower I4 after enrichment with hydrocarbon gases entering through the valved pipe 39. These gases may be natural gas, tail gases from cracking stills, water gas or any other suitable combustible mixture containing hydrogen or hydrocarbon. After passing through the drying tower the gases are s,

preheated and converted in the same manner as described in connection with Fig. 1. The added hydrocarbon or hydrogen content is large enough to increase the heat of reaction in the converter suiciently to maintain an adequate temperature. The acid mist leaving the absorption tower is precipitated by aV Cottrell precipitator or taken in a coke box.

The invention has been described specically in conjunction with a sulphuric acid absorber and electrostatic precipitator. This modication is the most economical and the simplest for most installations. However, it is not essential to use the ordinary type of sulphuric acid absorber, and

where acid of high purity is desired, and the f extra expense is warranted, the absorber may be entirely dispensed with and sufficient steam mixed with S03 gases from the converter so as to unite with all of the S03 to form sulphuric acid. The condensation of the acid, of course, has to take place in completely acid-proof equipment. For example, equipment made of silica or provided With a suitable acid-proof lining. This method of direct condensation of sulphuric acid is not claimed per se in the present application, as it is a well known method and is described, for example, in the patents to W. S. Allen, No. 1,771,520 of July 29, 1930 and No. 1,865,607 of July 5, 1932. It is an advantage of the present invention that it can be utilized in conjunction with any suitable acid condensation equipment which will permit operation with a moisture content such as to normally result in acid mist, and modications which do not use the conventional sulphuric acid absorber are therefore included.

4'" Y Y* Y faoeaves i j' Not vonly VVdoes'the presentiinvention eliminate equipment which would be otherwise required for removing hydrocarbon gases', partly or wholly, but itpresents a further radvantage oversystems in which/the' hydrocarbon gases are removed, inas-V muchwas'these systems are apt rto produce some free carbon or 'tarry material which may conl taminate Vthe drying tower acid. For many'purposes itis desirable to obtainall of the acid as a water-*White product.'Y and for such plants,4 the 1 Y presentinvention is particularly advantageous.

*I claim:

1. A process of'producingsulphuric acid-*which comprises'subjectingaa gas containing SO2, sufficient oxygenvto'permit oxidation of the SO2 to i S03, and agaseous combustible hydrogen containing material in the gas having a hydrogen content greater than 3 milligramsper cubic foot to'oxidationinl asulphuric acid converter in the presence Vof a sulphuric acid contact massV at reaction tem-V V fperature whereby the SO2 is transformed into YVS03 and the hydrogenl content of the gas is oxidized to H2O, passing the reactedgases into` a d Vsul'phuric` acid absorber without permittingY the temperature to-fall below the dew point foracid fmist' andsubjecting the exhaust gasesrfrom' the f absorbertodry precipitationof residual acidmist.

V- 2. A'proc-ess oi producing sulphuric acid which comprisesY subjecting Yresidual sludge from the sulphuric acidrpurification of 'carbonaceous'ma-- terial to thermal decomposition with the formaition of 'a gas containing SO2, removing the major vportion of free wateryaporfromrsaid gas'permitting sufcient'combustible hydrogen contain- 35 t ing gasesv to remain in thegas sothat: the hydrogen content after adjustment of the gascomposition for! sulphuric Vacid conversion'exceedsf Y milligrams of hydrogen vper cubic foot, adjusting thecomposition of the vgas by the addition of oxygenrcontaining gas, passing the adjusted gas :stream at reaction temperature over a sulphuric N `acid contact mass in af'converter, maintainingthertemperature, ofthe converted Vgases above Y the dew point for acid mist, absorbing the gases'in va sulphuric acid absorber and subjecting the exhaust gases from the absorber to Vdry precipitation n of residual vacid mist.

3; A process of producing sulphuric acid which VAcomp-rises subjecting Aresidual sludge'from the sulphuric acidY purification of petroleum products i*to'thermal.decompositionA with the formation of Y ja gas containing SO2, Aremoving the major portion'of freewater vapor from said gas permitting f sucient Vcombustible hydrogen containing gases to remain in the gasA so that the hydrogen content after adjustment ofthe gas composition for sulphuric acid conversion Vexceeds 3 milligrams f of Vhydrogen per cubic foot, adjusting the composi- 'Y j tionof thegas bythe addition of oxygencon- Y co` reaction temperature over a sulphuric acid containing gas, passing the adjusted gas stream at i peratureof the A convertedv gasesl abovej the dew Y n point for acid jmist, absorbing the gases ina sul` tact` masslin a `cor'iv'erter, inaintainingfthe ltem-V phuric Vacid, absorber and subjecting the exhaust n gases from the absorber to dryjprecipitationV of 5 residual acidmist. Y' Y e i c "4.' A method according to claim-2 in which the Vuncondensable hydrocarbonc'ontentof the Vgases isv not reduced at. all after leavingrthe acid sludge Y still. Y

t Y Y Y Y 1o' 5. A method according to claim Brin which the uncondensable hydrocarbon 'contentuof the 4'gases is not reduced at all after leaving. the acd'sludge still. i'

6.1 A method'according to @miniem which the Vw acid mist is precipitated` electrostatically. 'Y

7. A method according'to claimB in which the acid mist .is precipitated' electrostatically; 3. vA method of 'producing sulphuric acid which comprises subjecting an acid sludge from thesul- 20 p-huric acid purication of petroleum'productsto thermal decomposition with formation of avgas? n containing SO2 by'subjecting acid sludge to the yContact of hot combustion gases, removing the Y K major portion 'ofrfree water vapor from the SQ: v25 Yi #gas permittinglsunicient combustible hydrogen containing gasestor remain' inthe gas-so Vthat the Vhydrogencontent after adjustment of the gas composition for sulphuric Vacid conversion exceeds Y residual acid mist.Y

9. Amethodaccordingto claimrS in which none 40 f Vof the hydrogen containing gases are Vremoved Yfrom the stream Vprior toits passage .through the converter. "i"

. 10. Y:A method of producingsulphmic acid from gases containing an SO2 concentrationinsunicient '45v Y* Vfor adequate heat maintenance` infthe converter,

which comprises adding to the SOzjgas suicient" gaseoushydrogen containing substances to supe l j plyenough `heat during the conversion toflmain-f tainV propertemperature conditions in the*V con- 50 vertenadjustingtheoxygen content of the gas A fori conversionofV the SO2 and combustione!l the j hydrogen containing material and passing the gas stream atrr reaction temperature over a' contact` Vsulphuric acid catalyst in a converter, maintain-lV 65 Y t ing the temperature of the converted gases above 'Y the dew pointV of 'acid mist, absorbing the gases 'in Y a sulphuric acid absorber and vsubjecting the exi-- hau'st gases from the absorber 'to dry 'precipita'-V tion of acid mist. l Y

Y c Y wervr CYRIL B. n 

